1. Field of the Invention
The present invention relates generally to a system and method for forming a polyurethane foam and, more specifically to, a system and method for forming a polyurethane foam that includes mixing an additive with a resin component prior to mixing the resin component with an isocyanate component to form the polyurethane foam.
2. Description of the Related Art
A foam dispensing system for dispensing spray polyurethane foam (SPF) includes a source of resin component, e.g., polyol, a source of isocyanate component, a proportioner for mixing selected ratios of the resin component and the isocyanate component to form the polyurethane foam, and a gun from spraying the polyurethane foam. The application of the polyurethane foam can, for example, be used for thermal insulation such as for appliances, buildings, marine floatation, coatings, and packaging.
In the distant past, foam dispensing systems routinely used third stream dosing equipment to allow for additions of blowing agents, typically gaseous chlorofluorocarbons (CFCs) such as Freon-11 and Freon-12, for improving yield and processing latitude for the spray foam. With the conversion away from CFC's to hydrochlorofluorocarbons (HCFC's) as blowing agents, one HCFC blowing agent such as HCFC-141b became the preferred blowing agent for the spray foam. Since HCFC-141b was a high boiling point liquid, it was possible to make spray foam based on HCFC-141b only. Therefore, spray foam equipment manufactures discontinued the manufacture of third stream dosing equipment.
In certain situations, it is beneficial to meter additives to the resin component before the resin component is mixed with the isocyanate component. Such additives can include, for example, hydrofluoroolefins (HFOs) as blowing agents, hydrofluorocarbons (HFCs) as blowing agents, gaseous blowing agents, flammable blowing agents, liquid carbon dioxide, water, fire retardants, cell openers, solid fillers, and/or catalysts.
Despite providing advantages, some additives that are mixed with the resin component to form a mixture can make the resin component/additive mixture reactive or unstable. For example, with the launch of next generation blowing agents, Zero Ozone Depletion Potential (ODP) and Low Global Warming Potential (GWP) blowing agents such as hydrofluoro-olefines (HFOs) have immediate shelf stability issues with one or more of the HFO molecules. As such, an unusable state of the resin component/additive mixture can be a state in which the mixture could rupture its holding tank, be in a combustible state, and/or not have a suitable chemical make-up for its intended purpose. When such an additive is metered into the resin component to form a mixture, the resin component/additive mixture reaches the unusable state after a given period of time.
In the case of additives that create an unusable resin component/additive mixture, the additive is metered to the resin component in a batch process. In other words, the additive is metered to the resin component in a temporary holding tank, i.e., a day tank, to form the resin component/additive mixture and is immediately used. The resin component/additive mixture that is not used before the resin component/additive mixture reaches an unusable state is discarded, which is economically unwanted. In addition, equipment to make such resin component/additive mixtures is often expensive and designed for use with only one additive.
Accordingly, it would be advantageous to develop a system and method for metering an additive to a resin component to form a resin component/additive mixture and using the resin component/additive mixture with an isocyanate component to form a polyurethane foam before the resin component/additive mixture reaches an unusable state.